how do I monitor for itraconazole toxicity in dogs being treated for blastomycosis?

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Itraconazole toxicity monitoring in dogs treated for blastomycosis centers on serial liver enzyme surveillance and therapeutic drug monitoring, with compounded formulations requiring particular scrutiny. Hepatotoxicity is the primary adverse effect to monitor. Elevated alanine aminotransferase (ALT) activity occurs in 26% of itraconazole-treated dogs with blastomycosis.5 Skin lesions with crusting, inflammation, and discharge are also a recognized adverse effect — in one reported case, these developed after 3 months of itraconazole at 5 mg/kg PO q24h and resolved after drug discontinuation.4 Itraconazole should be administered with food to maximize absorption; concurrent antacids, H2-blockers, and cholinergics are contraindicated.10 Therapeutic drug monitoring is recommended for all dogs on itraconazole, regardless of formulation. The therapeutic target extrapolated from human data is a trough serum itraconazole concentration of at least 0.5–1.0 µg/mL by HPLC.12 Compounded itraconazole (bulk powder) produces a mean serum concentration of only 0.5 µg/mL, and 95.2% of dogs receiving it have subtherapeutic concentrations below 1.0 µg/mL — compounded formulations should be avoided.7 Generic pelletized itraconazole produces a mean concentration of 8.3 µg/mL and brand-name produces 6.5 µg/mL, with no statistically significant difference between these two.7 However, 12.5% of dogs on generic and 12.1% on brand-name still achieve subtherapeutic levels, and 37.5% on generic and 24% on brand-name reach potentially toxic concentrations above 10 µg/mL — making individual monitoring clinically important in all cases.7 Liver enzyme monitoring should accompany each recheck visit. The veterinary literature does not specify a fixed monitoring interval for ALT in blastomycosis-treated dogs, but urine Blastomyces antigen testing is performed monthly during treatment in published protocols, providing a natural cadence for concurrent biochemistry.2 If skin lesions consistent with itracon